[R] how to test whether two slopes are sign. different?

Peter Flom flom at ndri.org
Mon Jul 21 14:50:53 CEST 2003

A couple people gave you technical solutions already.

My question would be, after you've determined whether they are
significantly different, then what?  Isn't the better question whether
the two slopes are different in a substantively important way?


Peter L. Flom, PhD
Assistant Director, Statistics and Data Analysis Core
Center for Drug Use and HIV Research
National Development and Research Institutes
71 W. 23rd St
New York, NY 10010
(212) 845-4485 (voice)
(917) 438-0894 (fax)

>>> Gijsbert Stoet <stoet at volition.wustl.edu> 07/20/03 10:51PM >>>

  suppose I do want to test whether the slopes (e.g. determined with
lsfit) of two different population are significantly different, how do
I test this (in R). Say for example, I found out what the slope
between age and number of books read per year is for two different
populations of subjects (e.g. 25 man and 25 woman), say using
lsfit. How can I tell whether the slopes are different in R. (And how
would I do it for regression coefficients?)

Thanks a lot for your help.

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